I just finished a mixture control mod., but am not absolutely sure it will work. It should work any time the fuel injection is in the open loop mode, but I am primarily interested in open loop at WOT. At WOT the fuel injection is in the open loop mode and the oxygen sensors in the exhaust are not monitoring the mixture. In the closed loop mode they do, and force maintain the mixture at 14.7:1, which is chemically perfect for combustion and near optimum for emissions. Between 12-13:1 is optimum for performance. My mod. is a linear potentiometer that is adjustable from 0-50,000 ohms(which is the approximate range of the IAT) and is hooked up in series with "signal lead" of the intake air sensor (IAT). When in the "0" position (and in normal driving) it reads the sensor at face value, which is true intake air temp. Crank it all the way on (or somewhere in between) just before you're going to do a WOT blast, and the PCM computer thinks the intake air temp. is around 10 degrees F, and should then richen the mixture at WOT.....hopefully to the 12-13:1 air-fuel ratio. Right after the WOT run, the pot. must be turned back to "0" or the PCM will start tracking the readings and begin its adaptive corrections. My "Holley Bible" says that there is about a 4% difference in mixture requirements for every 11 degrees F change. I think it will work better in hotter weather than when cool, because of the larger temperature difference. My preliminary figures indicate that it will have to be set 43 plus or minus 7 degrees of true ambient to get the correct mixture. I have taken resistance readings of the IAT at 32, 40, 60, 80 and 120 degrees, so I will have some idea what to set the resistance at. Any comments or input on whether members think it will work are appreciated.

 

So what you're saying is that if at WOT the POT may affect the IAT, but the PCM may readjust B & F until the ENG revs into oblivion and everything goes to SH...T?
Sorry, just showing my ignorance [&:]

 

PM,
What this adjustable device does is fool the PCM computer into thinking the intake air temperature is cooler than it actually is, and therefore, richen the mixture. At least, that's the intent. At wide open throttle the PCM does not monitor the 4 oxygen sensors that normally sample air-fuel mixure during normal (cruise) conditions. When the oxygen sensors are sampling mixture it continually tells the PCM if the mixture is rich or lean and adjusts it to 14.7 parts air to 1 part fuel, which is the perfect mixture for complete combustion. It will have no effect on the rev. limiter or any other functions of the PCM. If left fully on (coldest temp.) the PCM will eventually turn on the malfunction indiicator light (MIL) because it is continually finding a large difference between the ambient temp. sensor and the intake air sensor. They normally would be relatively close to each other. Hope this helps your understanding of my foolishness. Sounds good on paper, I think. Keep on tinkering!!!

 

that is some high tech stuff u just said. correct me if i'm wrong, but wouldnt u want a leaner mixture to improve power? more air less fuel? i'm prolly totally wrong cuz this is some next level stuff, that i dont really know about.

 

i agree with the chef, and if you think that 14.7:1 is rich you better rethink about that one. but what do i know i just run a 900+ H.P. viper. richer is safer and leaner is meaner.

 

thats what i was thinking. richer is safer, lean u run the risk of high temp and damage to the engine. turbos, superchargers, nitrous, basically add more air (more oxygen) which equals more power....from my understanding of the RT's motor, it is ran very rich especially at WOT. i dont think chrysler wants a bunch of roasted motors brought in under warranty...
i'd like to see u're results if u do figure out how to control the ratio. both rich and lean. keep us posted.

 

Magnuman,
When I had my RT dynoed it was too rich. see the chart here https://dodgeforum.com/m_185709/tm.htm
The higher power run was done with the hose between the throttle body and air box unhooked from the air box. My A/F ratio was into the 11’s most of the time.
I either need more air or less fuel.
If you device works could it also lean out the mix?
That should be worth a few horsepower. (If the knock sensor isn't too sensitive and starts taking out timing) This is where a cooler engine would help.

 

Oops,
I re-read your opening statement and it would appear to say you can only make the mix fatter.

Any idea's on how to make it leaner. Other than a small dose of NOS.

 

Like I said, 14.7:1 is the stoichiometric, or chemically correct mixture provides for complete combustion. This is why most vehicle manufacturers run their mixtures real close to this setting. It is a happy medium of perfomance and economy. This mixture also provides about the lowest emissions. With leaner mixtures of 16-18:1, your emissions (especially oxides of nitrogen (NOX) increase, as does economy, engine heat, and risk of engine damage. Performance will deteriorate at these mixtures. Go leaner than 18:1 and you may start getting lean surge, or backfire through the induction system which can be very harmful. Maximum performace is achieved in the range of 12.5-13.3:1 air-fuel ratios. At these mixtures, the "excess" fuel makes certain that all of the oxygen in the air is consumed. Another reason is that mixure distribution to all cylinders, along with fuel-air mixing is seldom perfect. When all the air enters into the combustion process, more heat is generated and heat means pressure the engine can convert to power. Sometimes, an excess of fuel beyond that which produces maximum power is used for internal cooling of the engine, as was indicated by another member above. The down side of these "performance" mixtures is the increase in unburned hydrocarbons and carbon monoxide. As for my gizmo, it will probably be fairly difficult to know exactly where to set it, but if all other settings remain the same I am looking at 43 plus or minus 7 degrees less than true intake air temperature should bring me into the proper range. This is figuring a 4% difference in mixture for every 11 degrees of temperature. I've already done resistance calculation off the IAT sensor for the following temperatures: 32, 40, 80, and 120 degrees. I'll do more, eventually for every 10 degrees, which will make it easier to know where to set the control. A guy on one of the other forums is going to do the mod. and said he will do dyno tests to see if it works. Hopefully, this will give us a good idea whether this mod. has any merit. Otherwise, we're just using the butt dyno. until someone goes to the racetrack and checks it out. I also don't want everyone to think I am a know-it-all, which I am not, so I will tell you that I've paraphrased a lot of this mumbo jumbo from my old "Holley Carburetor Bible", which contains a wealth of information in this regard. I use to study this book for hours and use to be quite a whiz with those ancient devices. Hope this clears some of the mixture thing up a little.

 

maneval69,
I hear you on the rich mixture. The shop manual says the PCM is suppose to maintain mixture at 14.7:1, and that is what I am basing my assumptions on. Others have also said they are running rich, especially when their RT is relatively new. There has also been talk of the so called "150 hr/7000 mi." wake up, or leaning out of the mixture. I know my mileage has increased since reaching the 150 hour point, but I couldn't swear there was a wakeup. I have about 200 hours/5000 miles on it now, and get 15-18 mpg in town and around 28 on the highway, at 60-70 mph. No one, to my knowledge, has posted dyno results on RT's with the higher hours/miles. It would be interesting to see if the mixture is in the range the shop manual says it should be on higher mile/hour vehicles. Yours, in the 11:1 range, is really quite rich and ought to be giving you some pretty lousy mileage....and is too rich for optimum performance. It would be possible to fool the system in the other direction (leaner/lower resistance), but you would have to take the IAT sensor out of the loop when you do it. This is because the resistances are inverse to temperature....that is higher IAT (true intake) temperature equals lower resistance (leaner mixture), and lower IAT temperature (true intake) equals higher resistance or richer mixture. So, if the true intake air temp. was 70 degrees, which the IAT sensor is truely reading, you will have to decrease the resistance. You cannot reduce it with the sensor in the loop, because it is already at a higher resistance. The way I am doing mine to richen the mixture is to hook the variable resistor in series with the sensor and increase (lower temperature/richer mixture) the resistance. I think I'd keep an eye on yours and see what happens when you get more miles on it. If it continues in that range I'd make a trip to the dealer. If it persists, maybe the O2 sensor(s) are bad or the PCM is not working correctly.